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Lymphoid
Tissues
Lecture 4, 13/9/2015
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What are lymphoid tissues
• Organised tissues containing immune cells.
• Where cells develop and mature,(primary/central LT).
• Where lymphocytes interact with non-lymphoid cells, (secondary/peripheral LT).
• Where cellular interactions and then initiation of adaptive immune responses
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Primary lymphoid tissues: (Central)
• Bone marrow: B cells maturation, Myeloid cells, NK.
• Thymus: T cells maturation
Secondary lymphoid tissues: (Peripheral)
• Lymph nodes• Spleen• Mucosal lymphoid tissues (adenoids, tonsils, Peyer’s patches etc).
Major lymphoid organs and tissue
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What do they do?
• Most important part of the immune system.
• Immune cell development and maturation.
• Gathering and destroying infectious
agents by mounting immune responses.
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Bone Marrow
• Origin of immune system cells
• Network of stromal epithelial cells
• Haematopoietic stem cells
• Growth factors regulate cell proliferation and
differentiation
• B cell maturation
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Haematopoietic stem cellsللدم المكونة الجذعية الخاليا
Three main lineages:
• Erythroid: Red blood cells
• Myeloid: Granulocytes,Megakaryocytes
• Lymphoid : lymphocytes, NK cells
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Haematopoiesisالدم تكوين آلية
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Bone Marrow Birds bursa of Fabricius (B cell maturation)
MammalsB.M. (B cell maturation)
Except:
Cattle + Sheep Payer's Patch (B cell maturation)
Rabbit Appendix
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Thymus
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Features and Functions 1
• Most active in childhood, atrophies with age.
• Composed of 1- cortex (immature T cells are many) 2- medulla (mature T cells are few)
• Medulla contains Hassall’s corpuscles (thymic corpuseles).
• T cell maturation
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• Secretes thymic hormones to attract T cell and
promote their differentiation.
• Rich in epithelial cells.
• Selects against self-reactive T cells.
Features and Functions 2
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Cells of the Thymus
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Thymus: Hassall’s corpuscle
Small spherical bodies in the medulla, composed of epithelial cells arranged around clusters of degenerating lymphocytes and macrophages.
• Unique to thymus
• Clusters of epithelial cells
• ? Remove apoptotic
thymocytes
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Tissues of the adaptive immune response.
Summary 1:
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Cells of the Adaptive Immune System
• B cells Bone marrowAb production
• T cells Thymus
CD4+ helper cells (Th1 and Th2) stimulate responses
CD8+ Cytotoxic cellsKill infected cells
Summary 2:
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Any Question?